Apple has reportedly issued new seeds of Mac OS X 10.6 (Snow Leopard) and Mac OS X 10.5.8 to developers that, at least in the former case, add functionality that was previously only shown at WWDC.

Per AppleInsider and sources close to the story, the new Snow Leopard seed, 10A394, officially provides just compatibility, reliability and security fixes but appears to give developers access to Expose’s integration with the Dock.

As demonstrated by Apple executive Phil Schiller earlier this month, the feature lets users click and hold on an app’s Dock icon to show the windows relating to that app in equal-sized, organized tiles. The simple change makes it much easier to find a particular window for a project, for example, without having to invoke a specific Expose shortcut. They can also choose to view a selected window at full size to determine if the content inside is what they want.

A new Xcode 3.2 build has been released in tandem with the Snow Leopard build.

The new Mac OS X 10.5.8 seed has apparently advanced four builds from its previous state, to 9L20. Apple appears to be quickly winding up development, as it supposedly hasn’t mentioned any remaining known bugs and has fixed just a few prior issues, such as problems with using auto-complete on CalDAV servers in iCal, Image Capture’s support for large files, and syncing Address Book with MobileMe.

Apple has also asked developers to focus their testing on low-level components like graphics drivers, power management and storage.